The only honest appraisal of what's happening to the world's climate is to
look at long-term trends

Confused? You have every right to be. On just one day this week, it was reported that the heatwave that has lit wildfires across Australia is so unprecedented that two new colours have had to be added to weather forecasting maps; that 2012 had been by far the hottest year on record in the United States; that the blue-chip World Economic Forum had identified climate change as one of the world’s most urgent dangers; and that, nevertheless, the Met Office had concluded that global warming had stalled.

Both sides of the ever more acrimonious climate debate predictably rushed to contrasting conclusions. Environmentalists hailed the US and Australian records as confirmation that dangerous climate change has arrived – with some displaying distasteful schadenfreude that two of the most climate-sceptic countries besides Britain had been hit. And sceptics claimed that the Met Office had “finally conceded” that “there is no evidence that global warming is happening”. Both, of course, were exaggerating.

The Met Office’s chief scientist, Prof Julia Slingo, insisted that “the warming trend has not gone away”, torpedoing any suggestion of such a concession. And indeed the report that caused the fuss suggests that heating of the planet has not stopped, but slowed. Published with typical “barbecue summer” bungling on Christmas Eve – leading to understandable accusations of attempts to bury inconvenient news – the dry “decadal forecast” concluded that on average global temperatures over the next five years were “most likely” to be 0.43C above the average for 1971-2000, slightly lower than a similar forecast last year, which put it at 0.54C.

Interesting, but not exactly dramatic, particularly since it suggests that the world is indeed getting warmer over the long term, if not as fast as had been thought. But sceptics raised the stakes by pointing out that the 0.43 rise was almost identical to a 0.4 increase in 1998. They claimed this showed that temperatures have not risen significantly for 15 years.

But that is statistical sleight of hand, comparing an average temperature expected over five years with one for a single year (and an anomalous one at that). As we all know, weather naturally varies: some years are warmer, some cooler – and 1998, as it happens, is the hottest the Met Office has recorded.

It is therefore often picked by sceptics to suggest that the world is not heating up, since by definition a line drawn from it to any other year on the temperature graph would go downwards. If, instead, you were to pick 1996, a relatively cool year, as the starting point, it would suggest that the thermometer has been rapidly rising – but that would be equally misleading.

The only honest way to make comparisons is on a longer timescale, and on that basis it is clear that every decade since the 1960s has been warmer than the previous one, and that average temperatures have increased markedly over the past century. But it’s also true that over the past 15 years or so, the rate of warming has slowed down.

No one knows why. It may be natural variation; there have been other periods – 1973-1980 and 1988-1995 – where global warming seems to have stalled, only for temperatures to resume their rise. Or it may be caused by the cooling effect of massive air pollution in China; but that would disappear once it is cleaned up. It might also be that the heating process may be about to go into retreat, but there is no plausible scientific reason why that should be so, and no evidence for it.

Yet it is also wrong firmly to attribute Australia’s heatwave or America’s unprecedented year to climate change. Weather’s natural variability has ensured that extremes have occurred – and records set – throughout history. Again, the only honest thing to do is to look at long-term trends.

But these suggest that something is indeed afoot. Days above 37.8C are now five times more common than between 1911 and 1930 and extremely hot summers are 10 times more widespread globally than between 1951 and 1980.

There is no doubt that the world has warmed, and that this will continue. Certainly, picking an exceptionally hot year from the past to suggest that the world is not warming is like asserting that summer will not come this year because the mild weather of the past week is about to be replaced by a cold snap.

CHRISTMAS TREES GIVEN NEW LEASE OF LIFE TO SAVE RIVERBANK

What to do with the old Christmas tree? Many councils offer to take the festive cast-offs and turn them into compost and woodchips – though just a tenth of the six million that decorated British homes this year are recycled in this way. But the greenest solution I have yet found is, appropriately, in Ireland.

Last year, conservationists put 400 of them along the banks of the River Dalua near Kanturk in north Cork – part of the Upper Blackwater Special Area of Conservation, home to rare species such as the otter, kingfisher and freshwater pearl mussel. The river’s banks were eroding by about six feet a year, smothering the mussels and salmon spawning grounds with silt.

The trees – contributed by the public in the first exercise of its kind anywhere, and nailed to willow stakes – stabilise the banks, while their branches trail in the water, slowing its flow. Though it’s been a very wet year, with the river often in flood, they’ve done the job.

So far this week, local people have brought in another 700 trees to extend the EU-sponsored project. The organisers have just one request: “Remember to remove the tinsel and fairy lights.” Sounds like a plan.

SADLY, MR BOLES IS BUILDING HIS ARGUMENTS ON SAND

Honestly, I did not mean to write about Nick Boles again. But the ebullient planning minister keeps popping up to attack – and distort – the arguments this newspaper deployed last year to stop the system becoming a free-for-all.

On Thursday, in an interview with The Daily Telegraph, he suggested that his opponents were trying to stop house-building, thus keeping up prices and preventing young people buying homes. But we’re not.

We agree that many more houses are desperately needed, building them would boost the economy, and – yes – some will have to go on greenfield sites. But planning is needed to put them in the right places.

Mr Boles’s attempt to seize the moral high ground would be more convincing if he were not intending to allow developers to “renegotiate” agreements with councils to build affordable dwellings.

By the Government’s own figures, this may mean that 10,000 needy families will lose the chance to buy a home. True, he has promised to throw some money at the problem, but experts say that will not make up for the loss.

Does he care more about making housing affordable, or pleasing developers who make bigger profits from more expensive sales?